hi,  looks like you have developed folliculitis ( pyoderma)over your axilla.   Folliculitis (also known as Hot Tub Rash ) is the inflammation of one or more hair follicles. The condition may occur anywhere on the skin with the exception of the palms of the hands and soles of the feet. They may appear as red dots firstly and then increase in size to become red , hot, tender pus filled lesions. Avoid touching it too much. Avoid using any kind of cold dreams or hair oils, as it might increase the lesion. You can start using any topical antibiotic/antiseptic cream over the lesion and see if it persists even after using the cream for 2-3 days, then you need to consult a skin specialist as lesions on the scalp are very painful and also they tend to increase in size very quickly. Take some pain killers along for relieving the associated pain and discomfort.   Hope it helps  Dr Geetika Paul